Dave's Tech Blog

Filtering Silly Putty

noreply@blogger.com (Dave) — Sat, 12 Sep 2015 01:31:00 +0000

Years ago, probably about 1995 or thereabout, I hosted a 100lb Silly Putty group buy. I wrote a little web page using JSP, Perl, and Firebird, and used it to let dorks like myself sign up to buy Silly Putty in half-pound increments. I think I ended up with about 25 orders ranging from half a pound up to 15 pounds. Once we reached that magic 100lb aggregate, the minimum order quantity for Dow Corning® 3179 Dilatant Compound I had everyone mail me a check, and ordered a box of the stuff.

Not long after the boxes showed up I and one of the guys from the buy, a Cisco engineer from Austin, spent an evening dividing it up according to the order list and packing it into cardboard boxes for shipping. New 3179 Dilatant Compound is tough stuff, dividing it up is a tough forearm workout!

That was so successful I hosted a second buy for unpigmented translucent putty and a kilo of green glow powder to make glowing putty.

So, tl;dr: that's how I ended up with about 8 pounds of coral Silly Putty, several pounds of white putty, and a fist-sized blob of glowing putty.

The problem with Silly Putty is that over the years it collects lint and grit which makes it less fun to play with, and it darkens, especially if you like to use it to pull ink off of newspapers. So I was thinking of ways I could clean it. Picking out lint and grit is too slow to be realistic, but bulk filtering is impossible because it's a putty. But what if I dissolve it first and then filtered it?

I have a new bottle of Ronsonol lighter fluid that I bought as a home lab solvent a while back, so I figured I'd give it a job. I dropped a small blob of putty into a 20mm test tube, threw in a couple of tiny magnets to act as a stir bar, covered it in a few mL of lighter fluid and loaded it up on the stir plate:

I let it run for an hour or so, but the big chunk wasn't dissolving very fast, so I added a hot water bath to encourage it. Eventually, and with a little encouragement from a glass rod, it all dissolved into a clear solution and the coral pigment.

I centrifuged it and transferred the clear solution and the coral mess to evaporation dishes in the vent hood. After driving off the solvent I was left with unpigmented putty base and the coral pigment with it's contaminant load of lint and grit:

However, as you can see, the solids were a gummy mess. This is because I did not rinse the solids with clean solvent before evaporating the solution, which means that some of the putty base was left behind.

So I repeated the process with the gummy mess, this time rinsing, centrifuging, decanting twice more before drying the solids. The result is a very fine coral powder with some contaminants that I've halfheartedly manually separated.

I don't have a good way to divide the coral powder to show how small the particle size is, but it's talc-like. If I can get it down to fine powder I will be able to run it through a mesh to remove the remaining lint, and then I can incorporate it back into the putty to achieve the original goal, filtered putty (with only a faint smell of lighter fluid). I may try this again with a different solvent, maybe something that smells nicer. I'm sure alcohol will work, and it's easier to evaporate.

Van Overhead Console

noreply@blogger.com (Dave) — Tue, 17 Feb 2015 02:58:00 +0000

I'm building a new overhead console for the '93 B250 conversion van I've recently acquired:

After driving it around a while I decided that it doesn't have enough storage up front, and there isn't a good place to mount my FT-8800 amateur radio transceiver. A good way to fix that is a new overhead center console. Fortunately, all the interior trim is oak, so it's easy to match the existing style.

The roof of the van is 3/16 OSB, or something similar, in two pieces with a gap running down the center. The gap is covered by a third piece which is attached to the ceiling and holds everything up.

To that center piece I've attached some LED lighting, to brighten up the interior:

One of the problems with this is that the center strip is visible if the rear view mirror is angled upward a bit. This means that in the normal viewing position the night-mode reflection is pointed up at the LEDs, producing a ghostly reflection. The sight-line from the mirror to the rear windows is about four inches below the original center console, which means that if the new one comes down just less than 4 inches I won't be able to see it, but it will block the view of those LEDs.

This is the original upper center console. It's just a 3/4" oak plate.

The first step is to mock up the shape of the new console so I can drop it as low as possible without interfering with the rear view mirror sight-line. Cardboard and packing tape:

That gives me an approximate template. A little sketching and measuring provides the details.

For construction I used a 4'x8"x1/2" oak board. The angled cuts for the side pieces were interested. I don't have a sled for the table saw that will make those safely, so I just carefully cut them with the bandsaw, clamped the planks together and ran it across the jointer a couple of times to clean it up.

For the trapezoidal bits that extend up into the recessed area above the front seats I reused the existing trim pieces.

I ran the old finish pieces through the jointer to take off the old finish and glued them on.

Unfortunately I made a construction mistake and built the whole thing a half inch too narrow. Rather than rebuild it I just ran it through the table saw and glued in a carefully sized piece. Then, after much swearing and fine tuning with the Dremel, it went right in.

At the rear one of the storage pockets is visible. There are two, one on each side. They don't match exactly, but you can only see one at a time anyway, so no problem. At the front is a red LED that shines down on the center console. Just in front of the storage pocket is space for the body of the FT-8800 radio. The face of the radio (removable with remote mount) will go on the side near the front, and the handset will be stored inside behind the radio face. I'll have to make a door of some sort for access to the handset. For that I'm thinking I'll just cut a hole in the bottom plate at the front and stick some magnets in there to hold it on.

The bottom plate is screwed on and can be removed without removing the entire console, which is screwed to the ceiling panels. This is so that I can mount the console on the ceiling and then connect the various power and antenna cables that attach to the parts inside, and then put the cover plate on.

What's in an Inexpensive Centrifuge?

noreply@blogger.com (Dave) — Sun, 28 Dec 2014 10:14:00 +0000

I've added a low-speed centrifuge to my lab equipment. It is a Chinese-made device sold on Amazon by Hardware Factory Store. It works well, I can recommend it if you need a basic centrifuge.

I was curious what was inside, what does $110 get you?

Looks like a 25W 110V universal motor and a NXP BT136-600E triac controller. The rotor is light aluminum sheet, and the motor is mounted with rubber isolators.

The control panel:

Has a speed control (top), power switch and indicator (middle) and a mechanical timer (bottom). Notice that this control panel is different from the external picture of the unit which uses an illuminated switch where this one has a separate light.

Details of the motor controller:

Just your basic triac controller.

I noticed that if I put 115mm centrifuge tubes into it the tub runs into something inside. I put a camera inside and closed the unit to see what the problem was:

Turns out that modified power indicator is in the way. I'll fix that by 3D printing some collars to hold the tubes up a little farther so that they clear the indicator.

Crystal Chamber PID Tuning

noreply@blogger.com (Dave) — Mon, 27 Oct 2014 05:15:00 +0000

Since I'm trying to use a PID controller to keep the chamber temperatures under control I need to tune the PID parameters. And since this is designed to run for hours at a time, and because I'm crap at PID tuning, getting it right it is very tedious. Also presumably I'll need to tune it differently for different chamber loads. A liter of water is going to behave differently from a 50mL of solvent, so I figure I may need to retune it several times for different uses.

So I set it up to dump the parameters so I can visualize the process. Nothing fancy, just CSV out the serial port to a log file, then into Excel so I can see what's going on:

I've run half a dozen trials while I learn how to do PID tuning. That image is from part of the process where I'm looking for a good Kp that doesn't overshoot. After playing with it for a while I decided that I might as well get the rest of the hardware and software done, then play with the fine tuning later.

Crystal Chamber Controller Interface

noreply@blogger.com (Dave) — Mon, 27 Oct 2014 04:43:00 +0000

The code I've been using to run the temperature controller for the crystal chamber so far has been pretty bare, just the core PID loop. I don't have it tuned yet, but it's generally functional, so it's time to start getting it in shape to be an appliance.

A while back I picked up some old IBM modems that were being retired from the modem pool at work. I was hoping maybe I could convince one to speak Bell 202, but that didn't pan out. Anyway, they have nice boxes and the front panel has a set of buttons and an HD44780 LCD controller, so I held on to it:

The box has a nice power cord and switch built in, so I will be able to just stuff everything inside and put a connector on the back for the heater and temp sensor wires. Then I can use different chambers depending on what size I need. I could also run set it up to run multiple chambers, it only takes a couple more pins to run additional chambers, so I suppose I could set up to run about three. Maybe for version 2.

I wired it up for the LiquidCrystal library, plugged it in and away it went. The controller is only good for 8 characters, so I've got it set up to cycle the display through each setting one at a time. Right now, that's the setpoint temp, the current temp, and the number of seconds left in the ramp.

I also noticed that at some heater PWM frequencies the power supply squeals, so I added start and end cycle beepers. When I switch power supplies I'll probably need to add an actual beeper, but this was kinda fun in the meantime.

I also mounted the heater and temp sensor for real:

It's there at the bottom of the image. I used poly tube standoffs to keep the leads from contacting the aluminum tape and to provide a relatively stable mounting to the foam. The temp sensor is in the upper right-hand corner. Previously it was just laying on the floor of the chamber. Keeping it up in the warm air rising off the heater helps the response time, but also makes it clear that there's some pretty strong stratification going on in there. I'm pretty sure I'll need to add a tiny fan to keep the air mixed. I didn't want to do that because of the possibility for vibration to affect the crystals, but if it does end up being necessary I can probably isolation mount it somehow. Or maybe I should use an ionic wind type fan. Every project needs some nice high voltages, right?

The next step will be to scare up a new power supply that'll fit into the old modem box and come up with a connector for attaching the chamber.

Crystal Chamber Temperature Controller v0.1b

noreply@blogger.com (Dave) — Mon, 20 Oct 2014 20:45:00 +0000

I cobbled together a simple temp controller to try to get a feel for what it'll take to make one that will work for my temp controlled crystal-growing chamber. For this first iteration I've just got a simple PID-controlled heater, LM75 I2C temp sensor, and a 25W heater element.

For now I'm just running on an Arduino and a crappy bench supply (with a way-too-bright power indicator). For the finished project I'm thinking I will use a Teensy 3.0 as I've got some samples of them that I'd like to do a write-up about.

To house the controller I'll be repurposing an old modem that has a front panel with a small LCD and a set of buttons that I can use for menu navigation. I can mount a power supply and all the electronics inside and put a connector on the back that plugs into different chambers. This big chamber will be nice for large beakers, but I'd like to have a smaller one for test tubes. I can put a resistor on the chamber side of the connector so the control box can identify which chamber is connected and select the appropriate PID tuning.

I ran this for a few hours to see how it behaves. The 0.5C resolution on the sensor is pretty bad, but overall the results were encouraging. I don't really care much about how it handles large rates of change, since the hot solution will go into a preheated chamber. The main concern will be whether it can hold a stable downward ramp with minor fluctuations outside the chamber. I haven't tested that yet.

Next step is to get the heating element mounted so it is stable and out of the way and then test with a beaker of hot water so I can see how well it do temperature ramping. I'm pretty sure I'll need to upgrade to a higher resolution sensor for really long ramps, but for a day or two this 0.5C should be ok if I screw with the PID tuning enough.

The PID library has some kind of auto-tune that looks interesting, but I haven't figured out how to use it yet.

Insulated Temperature Controlled Chamber

noreply@blogger.com (Dave) — Wed, 15 Oct 2014 19:09:00 +0000

For my crystal-growing I'd like to have better control over temperature so that I can cool solutions very slowly. I've been using a heavy ceramic dish and a hot water bath for this, but I want to try cooling rates of days or weeks. To achieve that I think I'm going to want heavy insulation, radiant barrier, and probably a small computer-controlled heater element.

As a start I'm using 2" pink foam with aluminum tape as radiant barrier on the inside surface:

The foam is rated R-10. I'll put a liter of hot water in this and log the rate of change to get an idea of how much it reduces heat loss over open air. That should give me an idea of how much power I'll need the microcontroller temperature controller to handle.

I'd like to be able to keep it as low as 0.1degC per hour while minimizing fluctuations, but at this point I don't have any idea how challenging that will be.

Update:

As described above I put a 1 liter beaker of hot tap water into the chamber and stuck a thermometer through the top down into the water. I recorded the temperature every 10 minutes for a couple of hours, then wandered off for a while and then came back and got a final reading:

So I figure 1000L dropping 0.578C in 10 minutes is about 578 calories per 10 minutes, or 4.03 joules/second, 4 watts.

Room temp was 24C, and I was testing around 62C. The box surface is about 0.25 square meters, so that would be 4.03W/0.25sq.m, 16.1W/sq.m. R-value is ΔT/W/sq.m, so 38/16.1 = 2.36. The 2" pink foam spec is is R-10. Even with my shoddy construction I'd expect better than R-2.36.

Maybe that value is in RSI units. Wikipedia says the conversion from RSI to R-US is RSI * 5.68, so R-13.4. That sounds pretty reasonable considering the radiant barrier.

I might want to ramp the crystallization down to very cold temps, and it's a lot easier to just put the box in the freezer than it is to make a box that can cool itself, so the temp outside the box might be down at -20C. So, if I want to hold the box at 100C in a -20C environment, how much power do I need? Flipping the equation around and using the RSI value of 2.36: W/sq.m = ΔT/R, ΔT is 120C, so: 120C/2.36 = 50.9W/sq.m, or 12.7W for the 0.25 square meters of the box. Within my ability to measure that's linear scaling, which seems pretty reasonable from eye-balling the graph, which is also pretty linear over this narrow temperature range.

I'll give it some headroom and call the target 15W. On a 12V power supply I'll need to switch 1.25A. I've got a pile of IRF540N that'll be fine for that. My power supply is 12V at 3A, so my heating element needs to be between 4 and 10 ohms. Too low and I'll send the PSU into protection, too high and I can't get enough power out of it. That's probably another junk-box item.

Next up is electronics. I've got some old LM77 temp sensors laying around. They're not very accurate, but they'll be fine for a first iteration.

Update:

Started prototyping the controller:

The chip is an LM75 I had laying around. It's only 9 bit with the LSB reporting 0.5C increments. That's fairly awful, but it's good enough to get started. I can swap in a better sensor later.

I dug up an old nichrome toaster element to see if it would work as a heater:

I connected it to the desktop supply (which seems to be running 15V open-circuit, I may need to get in there and see what's going on with the regulation), and it runs at 13.7V and 2.05A, for 28.1W. That'll be perfect, I just need to put a MOSFET on to drive it and I should be able to hold the chamber at any temperature I like.

The insulated board it is wrapped around is 5 inches across which is just right to fit inside the chamber. I think that if I leave it on the board I can put it on one side of the chamber so that convection will prevent any stratification. I'll probably use one of the other toaster elements which is wrapped with all the turns on one side. I can face it toward the wall to create a chimney while avoiding radiant heating of the solution, That could definitely disturb crystal formation.

Crystals

noreply@blogger.com (Dave) — Sun, 05 Oct 2014 19:08:00 +0000

Recently I've been playing around with growing crystals. It was always a fun and easy thing to do when I was a kid, so I thought I'd try some that are more interesting than the usual salt, sugar, alum, epsom, etc.

This is recrystalized acetylsalicylic acid, asprin, from OTC tablets. 10g pulverized, washed with cold water, vacuum filtered, then dissolved in 250mL of 75C water and allowed to cool slowly. Crystals approximately 3-5 mm in length. I will chill this and allow crystal formation to finish, then wash the crystals and recrystallize at a slower rate.

This is benzocaine, extracted from Oragel tooth gel. 0.5g of gel stirred in 15mL cold water until dissolved. Benzoncaine will form white flakes. Centrifuge and draw off supernatant. Add 20mL water and heat in hot water bath. A bead of molten benzocaine will form. Add sufficient water to dissolve the bead. Allow to cool and crystallize. Vacuum filter and collect for recrystallization.

This is what I think is probably salicyclic acid. 1g of OTC tablets, pulverized, heated in 20mL water until dissolved. When cooled the entire 20mL formed one huge crystal block, which was amusing. Melted again, added 10mL water and heated until acetic acid formed. Cooling produced fine, hair-like crystals, which I suspect are salicyclic acid (more research to do). Washed and vacuum filtered, will recrystallize to see if more pure crystals look different.

Update:

After filtering and cleaning a bit more (there were still some components of the asprin tablets in the solution which affected crystalization), I got some recognizable salicylic acid crystals:

I was hoping to get some more acetylsalicylic acid crystals, but I accidentally hydrolyzed them. I'll have to give that try again later. For now I'm bored with salicylic acid, needle crystals are hard to photograph. I think I'll move on to something else.

Update:

I had a couple of 50mL beakers with more ASA and SA crystallizing by evaporation. One had mostly SA dissolved in a small amount of isopropanol, and the other was water. They've been sitting for about 5 days doing nothing, and apparently just reached the point where crystals could form. They went from nothing to quite a lot of crystals very quickly.

This one started out with what I think is SA making little needles at the bottom. I left it to evaporate and a few days later this big block formed overnight. I'm not sure if it's ASA or SA. The size suggests ASA, but I'm not sure how completely I hydrolyzed this solution, so I don't know how much of each compound is left. I'm going to let it keep evaporating and see what happens.

This one is the alcohol. It's evaporating faster than the water, and it wants to crawl up the sides a lot more, so it's probably not as likely to make crystals that are as nice. I will probably let this one go for a while until the alcohol is mostly gone and then rinse the crystals and redissolve them in alcohol and try again but with slower evaporation.

Macro Images of a Chip

noreply@blogger.com (Dave) — Mon, 24 Feb 2014 07:20:00 +0000

A friend from the Omaha Maker Group gave me an interesting chip a while back. Apparently it is some kind of optically sensitive chip, it has a clear case.

I thought it would be interesting to take some macro photos of it and see if I could capture some of the details of the die. I started out with just some simple shots with the kit lens and extension tubes.

Easy enough to see, but lighting was difficult with the chip as close to the lens as it was. You can see the wires and a little detail of the chip, and the lighting in this one gives a nice shadow on the wires.

I then switched to my long telephoto lens, extension tubes. This let me move the chip back from the lens a few inches, which made getting light in much easier. It didn't produce an image that was any more magnified though.

The chip is about 2.5mm on the short dimension.

From here I added a 10X macro expander lens and also a 10 triplet hand-lens to see if I could get any closer. This was difficult because it's a separate lens and can't easily be mounted on-axis with the camera lens. With a little fiddling around it came out ok. I can see a lot of details, though it's starting to get fuzzy around the outside, only the middle is relatively free of aberration.

Here's a crop from that image.

In the original photo the 2.5mm chip is a bit over 1100 pixels across, giving about 2170 nanometers per pixel. The narrowest traces are about 4 pixels wide, about 0.0003 inches. I'm not sure what the aperture was set to, but this is probably not bad performance for a first attempt. I'll have to do some reading and set up my equipment a little more carefully and see if I can sharpen this up a little more.

Edit: with a little more fiddling I got it down to 580 nanometers per pixel. Pretty sure I can take it farther, but I need to set up something to handle adjusting the sample position for fine focus. It's pretty fiddly. Also need to get some bright light onto it so I can see it in the live view. My dim desk lamp doesn't really cast enough light for this.

Photographic Depth of Field

noreply@blogger.com (Dave) — Sat, 22 Feb 2014 18:37:00 +0000

I was curious why a large aperture on a lens reduces depth of field. To investigate this I set my camera up with a macro extension tube and a subject with lots of depth.

The subject is a potassium sodium tartrate (Rochelle salt) crystal mounted in a brass holder, with a copper contact wire for detecting the crystal's piezoelectric properties. From the perspective of the camera, this setup looks like this:

This image shows a very short field, as is typical with macro photos that are taken from very close to the lens. The focal plane is about 10 degrees off of perpendicular from the surface of the coins, and intersects the subject about where the copper wire wraps around the crystal.

To understand why some parts of the image created when the aperture is large are blurry, it's helpful to visualize the paths the light takes through the lens. I used this simulator to make a simple diagram:

From any given point on the subject on the left, light passes through every point on the lens and is focused onto the camera's sensor. If you imagine a tiny bug with an equally tiny camera walking around on the big lens and taking his own pictures of the subject, you would noticed that depending on where he was standing, his photos would each be slightly different, sometimes from a little higher or lower, or one side or the other. We can simulate the bug camera photos by taking a picture through a pinhole placed in front of the lens.

Because the tiny bug camera has a really tiny aperture, all his photos will have very large depth of field, they'll be sharp all over. My bug-simulator has a fairly large pinhole, you can see it near the top of the image, it's about 2mm wide, so I won't get as much depth of field, but you can definitely see that much more of the depth of the image is in focus, compare to the image above and note how in these both the rubber band near the back of the image and the reeds on the edge of the coin are sharp. Here the bug is walking from one side of the lens to the other:

It's hard to tell in the still images, but the perspective is different in each shot, the angles all change a bit as the bug walks across the lens. It's easier to see this if you user a bigger hole so that you get a full-frame image instead of the circular shot, but it's harder to see the increase in the depth of field. Here is another example with a slot to let in more light. Left side from the top of the lens, right side from the bottom.

Since the tiny bug camera can only collect a tiny bit of light with each photo, all those slightly-different photos will be quite dark. If we stack them all up to increase the brightness, we get the image we would get from the regular-sized camera. It's a bright, but only the parts that were all the same in the individual images will still look sharp in the combined image. The parts that were all slightly different will be all mixed together, making them appear blurry.

That's exactly what the big lens is doing, stacking together thousands of different perspectives of the view all taken at the same time. We could get deeper depth of field in the image by using a smaller aperture, but that makes the image darker. To compensate we can increase the light on the subject, leave the shutter open longer, or use a more sensitive sensor.

To really see this effect, it's best to see it in a video, so check this out:

Wattvision Meter Reader

noreply@blogger.com (Dave) — Tue, 15 Jan 2013 19:47:00 +0000

Just a quick note about the Wattvision electric meter reader product. I haven't seen one in person, I was just reviewing the website, but this looks like about the simplest solution out there right now. I still like the idea of the RF approach, but visually inspecting the options on the meter is a good option too.

It's a little spendy at $250, but I suppose that's not too bad if it gives you the online tools and such as well. I think that a maker could easily hack together the same system with an Arduino and Wifi shield or Rasberry Pi and Wifi for under a hundred. And I think a couple of AVRs and a cheap RF serial link could do the job for about $30.

Underfloor Vacuum

noreply@blogger.com (Dave) — Thu, 20 Dec 2012 02:31:00 +0000

As a fun afternoon project I decided to try turning an old retired vacuum into an underfloor vacuum system. The idea is that when I'm dust mopping in the dining room and kitchen, rather than picking up with a dust pan, I can sweep it into a vacuum intake on the floor. This probably is not any easier than using a dust pan, but it's more fun :)

Also, I figured that rather than using the regular vacuum bag, I would experiment with using a vortex bucket to collect some of the trash, rather than filling up the disposable vacuum cleaner filter bags. I have no idea what it takes to make that work, but what the heck, I'll take a stab at it. I've been thinking a dust collection system might be a good project for the workshop, and if a swirly bucket like this works, it would be easier to dump than a shop vac.

I started with a Gamma Seal bucket lid. This is a fantastic product for anyone who reuses 5 gallon buckets. It's a ring that seals tightly onto the bucket better than a regular lid, but the entire center is threaded so it's easy to unscrew it to get to the contents. I figured I'd fix the lid to the ceiling, run the hoses in through the central part, and then when I need to remove the bucket part, I can just unscrew it and leave the lid and everything attached to the ceiling.

The inlet has to be tangent-ish to spin the air, with the outlet in the center, so that hopefully the heavier particles will fall to the bottom before the air exits and goes to the vacuum. I cut out a pathway through the lid for some PVC tubing.

However, I couldn't have the end of the pipe sticking up where it would run into the ceiling, or pinch the hose, so I used the table saw to make it more flexable:

I bent it to the right shape and fixed it in place with some aluminum duct-sealing tape. Most of the lid is held together with this tape. If it all works like it's supposed to I might epoxy it down at some point. Until then the tape will be fine.

To mount the lid I cut a 2x4 to go between the floor joists and drilled a hole for the outlet.

The Gamma lid ring goes on the bucket. Takes a hammer.Not looking forward to taking that thing off again.

The assembled lid with hoses goes on the ceiling. The inlet hose goes through a hole in the ceiling and comes out underneath the front of the dishwasher. For another project I'll make a sheetmetal collection hood with an inlet about half an inch tall and 10 inches wide this will poke out just under the kickplate at the base of the dishwasher.

Finally, the vacuum cleaner. I don't know if this is going to work, so I'm just hanging it with plumbers tape. That should avoid coupling too much noise to the floor.

Obviously I still need a way to turn on the vacuum, which is in the basement, when I'm sweeping in the kitchen. So, X10 appliance module to the rescue. I have a number of wireless X10 controllers that I can use to switch the vacuum from the kitchen. So far so good.

Zen Toolworks 7x7 Home Switches and Sanguinololu

noreply@blogger.com (Dave) — Sun, 16 Dec 2012 06:57:00 +0000

I've been spending some time upgrading the Zen Toolworks 7x7 mill. I glued in some home switches and wired everything up to to the the Sanguinololu, and glued some split-loom onto the machine to route wires through. That all came out pretty nice. I mounted the board with some hook-and-loop on the back of the X axis, and placed the switches where the moving parts would contact them.

Here is the back of the machine, showing the Sanguinololu and wiring.

Here are the home switches, Z, X, and Y, respectively.

I was having some trouble getting software onto the Sanguinolol, it wasn't responding to the serial port. I loaded Triffids Teacup firmware on it using the Pololu AVR programmer, and it started sending the initial 'start' and 'ok' messages, but nothing after that. After fiddling with it a bit I hooked up the Bus Pirate in RS232 mode to check at the AVR pins to see whether the messages I was sending were making it through. They were not. Using the Bus Pirate to inject data directly at the AVR pin made it work as it should. This confirmed what I suspected, there was a bad connection between the AVR and the FTDI chip. I touched up the appropriate pins on the FTDI chip, and it started working normally.

So now it's time to start getting into software to convert designs into parts. In the past I used the DOS-based TurboCNC program to control my machine, and previously I was running this machine using it. However, I didn't want to be tied to an old computer with a parallel port, so I decided it was time to move to a USB-connected external board, which is where the Sanguinololu comes in.

I had the option to use a number of Sanguinololu-compatible firmware packages, and I've started with Teacup. I had Kliment's Sprinter on it previously, but I switched to Teacup when I couldn't get Sprinter working (because of the bad solder connection). Now that I've put the effort into configuring Teacup, I'm kind of hoping I don't have to try a different one. Unfortunately, Teacup doesn't support G2/3 arcs, which kind of sucks. I may switch back to Sprinter or something so I don't have to decompose all my arcs into line segments. This would work, but because the ramp acceleration mode does a full start and stop for each segment, it would be very slow. RepRap acceleration mode would get around this, but it's kind of a weird mode that requires the software generating the gcode work a little differently. I'd like to use Grbl, but I'm not sure if it is compatible with the Sanguinololu. I'll have to look into that a little closer.

One of the nice things about TurboCNC is that it has a fairly rich set of gcode commands that make it easy to run existing gcode files that include features like loops, printing messages to the screen while it waits for you to switch tools, tool offsets, fixtures, etc. Teacup doesn't have these, and I kind of like those features.

So, to address this, I've taken the TurboCNC source code, which is normally compiled in Borland Turbo Pascal under DOS, and pulled it into Delphi7 and generally torn it into itty bitty bits. I removed all the UI code (which was based on a third party library that worked similarly to the TurboVision UI package), and eliminated all of the stepper code, and kept mostly the gcode handling routines. I replaced the calls to step-generation routines with calls that output basic gcode commands, which allows Teacup to handle the step generation. I've also added an OpenGL-based tool-path viewer, so it's easy to do a dry-run and see if it looks sane. The viewer will track what has been sent to the machine, but it doesn't yet watch for the block-completed messages, so it isn't very smart about knowing where in the list of queued commands Teacup is. This really only shows up when making long moves, but it would be nice if I could make it more precise.

At this point it will handle some gcode features that Teacup will not (loops, gotos, etc), and does not decompose arcs into line segments (I'll have to add that as a feature for completeness, as much as I'd prefer to have it in hardware), and showing messages while waiting for the user, but it's still missing some of the more advanced features that I want it to have. In particular I'd like to get it working with a touch probe.

Here's how it looks after running a simple sample file:

For testing purposes I just have it output the generated gcode to a text file that I feed to the machine with a debug terminal. And, since I don't want to get it mounted with a cutting tool yet, I figured I'd make a little ballpoint pen attachment that fits in my Dremel Flextool holder:

While I was looking around on the web for something I ran across the TkkrLab wiki, where they are building pretty much the same setup as I've got here. In fact, I was surprised to see a link at the bottom of the page back to my flexshaft mount blog post :) It looks like they've run into the same problem with Teacup not supporting arcs. I'll have to keep an eye on their progress and see if one of the other options works for them.

Anyway, here's the mill running the sample file:

If you compare to the tool path preview in the screenshot above you can see where it skips the G2/3 arcs. Other than that it's working fairly well. At this point I probably need to spend some more time working on my Windows derivative to TurboCNC, and maybe see what I can do about evaluating other firmwares with arc support.

3D Printed Model Airplane Motor Mount

noreply@blogger.com (Dave) — Sat, 17 Nov 2012 22:17:00 +0000

Last time I had my plane out to fly I had a rather hard landing that broke the motor mount. I expect that I'll probably do that a few more times, so I built a model of a mount and 3D printed a few of them on the Omaha Maker Group's 3D printer. I made the model to the exact size, so I had to do some filing before I could get it to fit properly. I'll have to keep the oversized printing in mind next time.

The plan is for the mount to break along the print layers next time I crash, to avoid damaging the motor shaft. I'm sure that plan will be tested.

Dremel Flex-Shaft Mount for Zen Toolworks 7x7 Mill

noreply@blogger.com (Dave) — Tue, 13 Mar 2012 01:03:00 +0000

I wanted to try out AutoDesk 123D for designing parts to be 3D printed on the RepRap, so I designed a holder for a Dremel Flex-Shaft so I can mount it on my Zen Toolsworks 7x7 Mill.

Drawing the model in 123D was fast and easy. I'm looking forward to using it for other things. I constructed this by starting a sketch in the XY plane and drawing the long rectangle, the two concentric circles for the holder part, two three-point arcs for the fillets (it may be able to do that automatically, I didn't experiment with that), and a couple of rectangles for the tabs. The sketch lets you multi-select the areas defined by the lines, so you can then extrude just the parts of the sketch you want. For the horizontal holes I started sketches on the faces where the holes needed to be (just a circle), then push/pulled it through the solid. Very simple construction process, and it maintains all the sketches and push/pull operations in the Browser, so you can easily go back and change them later.

I drew all the holes to the exact size. I know that the RepRap typically makes the holes a little small, but I wasn't sure if it would be better to draw them a little bigger or drill them out.

Once I had the model done I saved it as a .stl file and got it going on the printer. This is about as easy as it could be. The printer has home switches on all the axes, so it's just a matter of opening the file and clicking 'print'. It takes it a minute or two to warm up, then it's off and printing.

It took about 15 minutes to get both parts printed. They came out pretty good. The horizontal mount holes are only 5mm from the edge, and I noticed that the layers were a little wobbly on that narrow part, but nothing serious. I think in the future I should probably try to provide more material around horizontal holes like that.

I ran a drill bit through all the holes to bring them to the target size. It seems to make them about 0.5mm too small. That works out pretty well because the drilled surface is more precise and smooth anyway. Since the back of the part that mounts to the tool plate on the mill is a bit wavy I decided I'd face it on the mill to make it flat and square with the bottom of the part( which is glass-smooth from the bed of the printer).

Milling the plastic part works pretty well, but you have to be careful to not go too deep. Because the interior of the part is an open network (I'm using 30% fill) you can't cut away very much wall and retain the strength of the part. Also, where the filaments stick to each other isn't nearly as strong as the plastic itself, so if you try to cut nearly through a layer it'll tend to peel off in strings. It's probably best to plan to cut not more than halfway through the filament depth, or possibly to impregnate the part with epoxy (or maybe wax) before milling. I ran the parts on the big mill with a fly-cutter, and other than tearing up a few filaments, the milled face came out great.

Mounting the part on the mill was fast and easy, all the holes were exactly where they were supposed to be, and it was all square and flat. It bolted right up and is good to go.

Fortunately, my Flex-Shaft is the old-style with a simple 12mm tube, so no funky ergonomic shapes to deal with.

I think next I'll make an adapter plate system with some magnets in it so I can quickly swap out simple tools, like a pen holder, magnetic field sensor, touch probe, etc.

iPod Macro Photos

noreply@blogger.com (Dave) — Tue, 24 Jan 2012 01:29:00 +0000

I ordered a couple of small lenses from Surplus Shed (#L4471) to try out as macro lenses for the iPod Touch. They arrived today, so I tried taking a couple of test pictures with them taped to the front of the iPod. I was a little disappointed, as I was hoping to get tighter close-up with it. So, naturally, I stacked the two of them together to try it that way. This is the result.

These are images of the pixels on my monitor (~92 px/in ) taken with the iPod and my DiMage Z2 in SuperMacro mode. The image resolution ends up being very similar (in this test each screen pixel ends up being about 12 pixels across), but the Z2 does a better job overall, with better color and, of course, more pixels overall. The iPod does pretty good though, certainly acceptable for quick shots of stuff. I'd like to try another lens with a different focal length (these are 51mm) to see if I can get up closer.

Here I got a picture of a US penny. The Z2 will take better macro pictures than this, but I didn't put any effort into setting up, I just snapped a handheld auto-focus picture with ambient light. But I did the same thing with the iPod, so it's a reasonably fair comparison of taking a photo under these conditions.

Web-attached pan tilt camera

noreply@blogger.com (Dave) — Thu, 19 Jan 2012 20:15:00 +0000

With some help from Brandon and Ben I got the mechanics for the pan tilt camera rig going. The servos attach to an Arduino which is connected to a computer running a Windows web service that provides access to the camera.

I had an issue with the movement speed initially, and had to update the Arduino code with some position speed ramping. That went well and it is moving more smoothly. It flops around a bit, but I think that is mostly the slop in the mechanism.

The web service supports tagging of positions so that interesting views can be labeled. Once labeled a single button press takes the camera back to the associated position.

I will post some video of it in action soon.

Mail Rings

noreply@blogger.com (Dave) — Sun, 15 Jan 2012 03:01:00 +0000

I'm working on a 4 in 1 mail wristband as a gift, and I thought it would be interesting to try welding and brazing some rings. This is the result, prior to an acid bath and more polishing. Unfortunately I ran out of oxygen before I could get very far with the brazing, and I didn't manage to close a ring with the brazing.

I deliberately picked some 'worst case' rings, which had wide gaps. These were fairly easy to close, and I think that well-formed rings would come out very nice.

I wouldn't want to do more than a few hundred like this, but I think smaller pieces shouldn't be too bad.

Tippy forge

noreply@blogger.com (Dave) — Wed, 11 Jan 2012 14:10:00 +0000

Here are a couple of videos of the tippy forge I've been working on for the Omaha maker Group. At this point it just needs the frame to hold it and a handle to make it easy to tip. There is a little leakage from the input that we need to get sealed up, but it works quite well so far.

Motor demonstration rig

noreply@blogger.com (Dave) — Wed, 11 Jan 2012 14:05:00 +0000

One of the interesting projects from the Omaha Maker Group meeting on Jan 10. Ben put together this little motor demonstration rig with a couple of magnets, a 3D printed frame, and the armature from a commercial motor. Here he is just holding a couple of wires against the commutator as brushes. It's interesting to see the effect of adjusting the brush positions relative to the magnets.

Arduino Fio and other bits

noreply@blogger.com (Dave) — Tue, 10 Jan 2012 17:38:00 +0000

Received an Arduino Fio and some other bits in the mail today. I was planning to use this for the Omaha Maker Group Makery Monitor Micro (OMGMMM), but I did not pay close enough attention when ordering and pdid not notice that it doesn't support the USB serial. I didn't have the budget for the XBees for it, but I guess I will have to do that sooner rather than later, as the web page and web services for it are getting close to beeing deployable. It even supports driving servos via the web service.

MakerBot DC Servo Controller and Quadrature Divider

noreply@blogger.com (Dave) — Tue, 23 Aug 2011 21:33:00 +0000

I've been working on putting together the parts that will run one of the Makery robot arms for an art show. Part of this involves getting a MakerBot DC Servo controller working with the 1000 ppr servos on the arm. At moderate speeds the encoder output is over 25kHz, which is apparently too fast for the servo controller software. If the encoder output changes at all the controller gets confused and runs away.

To address this I loaded a 3 channel quadrature divider program onto an ATmega168. This will divide the quadrature pulse stream by 16 (it is configurable, powers of two up to 16), which should make it slow enough for the servo controller to handle it pretty easily.

I uploaded a video of it running, and added a bazillion annotation bubbles.

The next step is to feed it a pulse stream and see how well it responds.

Doorbell Upgrade

noreply@blogger.com (Dave) — Mon, 08 Aug 2011 04:51:00 +0000

Recently I discovered that my doorbell has become unreliable. The UPS guy never wants to wait around, and sometimes he takes the packages with him, so I had to do something about this problem. I picked up a new bell at the hardware store for a couple bucks, but it's a cheap plastic model, where the original is a nice heavy metal model with a light in it.

I took apart the old one to see if I could swap parts to reuse the nicer one, and found that the only part that was really a problem was the button, which has degraded on the side facing the afternoon sun.

Fortunately the new one is almost exactly the same size, so I swapped it in and had a like-new repair. Cool, 5 minutes and the job was done.

Of course, as soon as I reconnected the wires the little light bulb burned out. It's been running continuously for 5 years now, so I guess that isn't too bad a lifetime, but I'd like the button to be lit, so I'll need to get that little guy out of there and find a replacement.

I'd probably have to spend $15 on a new lighted switch to get one of those little 20VAC bulbs, so I'll be looking for something else. Twenty volts is a little low for neon bulbs and electroluminescent wire or film, so I guess it'll have to be an LED. Fortunately I've got a ton of those. Red would be neat, but maybe a little boring. I have a bunch of IR LED's and some luminescent powder, so I could coat the inside of the button and make it glow, but I'll probably have to replace it again in a few years, and I don't want to have to reapply the glow powder. So I think I'll go with one of the blue LEDs I had left over from my binary clock project.

The LED will need a diode to block half the AC voltage and a resistor to limit the current. I used 33mA for the clock, and that's plenty bright for this, so I found an ~800 ohm resistor for this.

There isn't much space in the doorbell, so I marked where the circuit board did not lay on top of the metal contacts, connected the resistor and diode and laid them out to see where I'd need new holes for the leads.

Looks like it will fit without much trouble. There is just enough room between the PCB and the wall to avoid squashing the resistor. I marked the trace where the new holes will go and drilled them out.

Then cut the trace between the new holes.

A little work with a needle file to make some new pads around the holes...

And I can solder in the new components.

Next the LED goes in, but first I lopped off the lens with the dremel to turn the end of the LED into a diffuser. There isn't enough room in the switch body to stand it up, and the beam is too narrow for that anyway.

Before I reassembled the switch I took the chance to bend the contacts into a higher arc so that the button only has to be pushed about 2mm to make contact. It was set for more like 3mm, which put the button almost inside the switch body, which was contributing to the difficulty of getting it to work.

I put it back together and hooked it up, and it's working as planned:

A neat improvement on this would be to replace the factory board with a custom board with an ATtiny13 and a couple SMT RGB LEDs so that the button could cycle through a set of colors. It would reset when the switch is pressed, so the startup code could do a neat flash of colors to indicate that it had been pressed before returning to the usual slow color cycle.

Motorized Potentiometer

noreply@blogger.com (Dave) — Sun, 07 Aug 2011 02:38:00 +0000

I had a broken micro RC car that used a gearbox with a tiny potentiometer on it for controlling the steering angle. I thought it would be interesting to replace the little potentiometer with a regular sized version so I could set the position either manually or from a microcontroller by driving the motor.

I drilled a bit of brass rod to fit over the gearbox output and to fit the stub of shaft on the back of the pot. I used some loctite and epoxy to connect the shafts together, and ran it a bit to get it all concentric, then epoxied a bit of aluminum strap to both.

The next step is to come up with some code to read the pot and drive the motor to the commanded position. Since it holds position without power to the motor, the h-bridge can be left idle except when it is moving to a commanded position, so that a user can turn the knob to adjust a setting.

Stepper Heat Sinks

noreply@blogger.com (Dave) — Tue, 02 Aug 2011 04:34:00 +0000

I've been using some Pololu A4983 Stepper Motor Driver Carrier boards to run the stepper motors on my mill, but I noticed the other day that they are overheating and cutting out briefly, even with a small fan blowing on them. This isn't surprising, since I'm not running them with any sort of heat sink. As a test I held a bit of brass rod against the top of one of the chips and the glitching went away immediately.

To make some heat sinks I decided I would cut down a heat sink I pulled out of some salvage equipment. Probably a computer monitor. I stopped by the Makery to use the sawzall and scroll saw to chop it up into suitably sized bits, then returned home to finish them off.

I spent some time with the dremel to make a 5x5mm pad on the bottom of the heatsink. I just eyeballed it, but the micrometer says they are all within 0.15mm of the target size, except one, which was off by 0.5mm. Not bad for eyeballing.

I didn't have any thermal tape, which would be perfect for this, so I just put some thermal compound on it to be a weak adhesive. I'll just have to be careful with them for now. Once I have the machine running with this cobbled-together electronics setup I'll use it to make something to mount the parts more robustly.

Now they just have to sit around so the heatsink compound can set up a bit.